Dopamine has been localized in high concentrations in the carotid body and has been hypothesized to be a modulator of chemoreceptor afferent activity. The object of the proposed research is to define the role of endogenous dopamine as it affects the response of the carotid body to hypoxia. We hypothesize that the dopamine secretion rate of glomus cells is a function of the activity of the afferent nerve endings. The proposed methods of study involve electrically monitoring the afferent sinus nerve activity in vitro under temperature-controlled conditions. The neural activity will be characterized by the techniques of information theory. The effect of temperature changes of the hypoxic response before and after dopamine antagonism, application of dopamine agonists and exogenous dopamine will be investigated in order to establish the relationship between the afferent nerve ending and carotid body glomus cell.